Insulated conductor



Dec. 28, 1943. J. R. PATTERSON ET AL 2,337,920

INSULATED CONDUCTOR Filed Nov. 28, 1939 FABRIC I/ARN/SHED WITH RES/N01,?REACT/0N PRODUCT OF PENTAER l/R/TOL FATTY OIL. ACID AND POLYSAS/C ACIDPROTECTIVE COVERING OF COTTON BRA/D Inventors. James Q. Patterson, JamesQ. Qeid, Harry A. Lethe on,

heir Attqrney.

Patented Dec. as, 1943 INSULATED CONDUCTOR James R. Patterson, Scotia.and James B. Reid and Henry A. Letteron, Schenectady, N. Y., asslgnorsto General Electric Company, a corporation of New York ApplicationNovember 28, 1030, Serial No. 300,520

1 Claim. (01. 174-121) This invention relates to insulated electricalcables and more particularly is concerned with an improved electricalinsulation of the varnished cambric type.

Insulated electrical cables or conductors have previously been preparedin which all or part of the insulation is made up of varnished fabrics,as for example, a fabric coated with a composition containing the usualalkyd resins composed of g-lycerine, phthalic anhydride and fatty oilsor acids. However, these insulated cables have not been whollysatisfactory-primarily because of the high power factor of thesevarnished fabrics at elevated temperatures.

We have now discovered that insulated cables of improved electricalproperties maybe obtained if the insulation thereon comprises a fabricvarnished with a composition comprising the resinous reaction product ofpentaerythritol, a monobasic organic acid, specifically the acids ofdrying, semi-drying or non-drying oils, and, in addition, a polybasicorganic acid or anhydride such as maleic, phthalic, etc. The low lossinsulation of this invention is characterized by a high dielectricstrength of above 1000 volts per mil, and a low power factor not only atordinary temperatures but also at such a high temperature as 100 C. Thevarnished fabric is smooth-surfaced and has excellent resistance to oil,moisture, abrasion and aging. The resin film contained therein is hard,flexible and tough.

In the accompanying drawing, we have illustrated one form of ourinvention in which a conductor l is provided with one or more layers ofour low power factor insulation 2 and an outer protective covering ofcotton braid 3, preferably varnish treated. It is to be understood,however, that our invention is not limited to this particular cablestructure. The outer covering may suitably consist of a layer of metalsuch as a lead sheath or strands of wrapped or woven steel wire or thelike. Again, other insulating materials than those mentioned above maybe used. For certain applications, it may be desirable to cover or coatthe conductor with a layer of asbestos, cotton thread, rubber, or anenamel before applying the varnished fabric. Or the conductor may beprovided with altemating coverings of the varnished fabric and any ofthese insulating materials.

In order that those skilled in the art better may understand how thepresent invention may be carried into effect, the following specificexamples are given for the purp se of illustrating the preparation ofthe varnish and the varnished fabric:

1 hour. The temperature is raised to about 235 to 250 C. and the resincooked to an acid number of about 5. The resulting resin is dissolved ina suitable solvent, for example petroleum spirits, in ratios such as toyield a varnish of the desired viscosity. Usually the varnish containsfrom about 50 to per cent by weight of solids. Driers are added and theresulting varnish is applied to cloth or other flexible material inaccordance with conventional practice. The coated cloth is usually bakedto harden the coating, but it can be air dried. The electricallyinsulating tapes or sheets are made by cutting the dried cloth to thedesired width and are applied as conductor insulation in the usualmanner.

All the ingredients except the maleic anhydride are placed in a kettleand heated for about 1 hour at approximately to 200 C. The maleicanhydride is added and the batch is held at 190 to 200 C. until a clearpill is produced. The temperature is now raised to about 235 to 250 C.and cooking continued until a resin having an acid number of about 5 isobtained. The maleic anhydride is not added until the other ingredientshave partially reacted, whereby a clear homogeneousresin will beproduced. The varnish and the coated fabric insulation are made fromthis resin in substantially the same manner as described under Example1.

Maleic anhydri 4 Essentially the same procedure is followed as describedunder Example 2.

Example 4 Parts by weight Pentaerythrltol 13.9 Soya bean oil fatty acids81.2 Maleic anhydrlde 4.9

The procedure is essentially the same as described under Example 2.

Example 5 Same as Example 4 with the exception that linseed oil fattyacids are used instead of soya bean oil fatty acids.

It is of course understood that our invention is not limited to thespecific ingredients other than pentaerythritol named above in theillustrative examples. For example, as monobasic carboxylic acids, wemay use in addition to those mentioned above the fatty acids ofChina-wood oil, perilla oil, fish oil, oiticica oil, etc., or mixturesof such acids. As polybasic carboxylic acids or anhydrides, we may usein addition to those mentioned above such acids or anhydrides as, forinstance, malonic, succinic, glutaric, adipic,

pimelic, suberic, sebacic, fumaric, etc., or mixtures of such acids oranhydrides. Maleic acid or anhydride is particularly suitable for usebecause it provides a further improvement in the power factor of thefinished product. Especially good results also are obtained by usingmixtures of maleic acid or anhydride with other polybasic organic acidsor anhydrides. The term acid" as used broadly in the appended claims isintended to include within its meaning the anhydride of the acid.

In making the varnish, the resinous composition may be thinned with anysuitable solvent, for example turpentine, coal tar solvents, petroleumhydrocarbon solvents, etc. Any suitable drier and in any convenient formmay be used, for example the naphthenates, linoleates or resinates ofmetals such as calcium, manganese, lead, cobalt, zinc and iron.' Thepercentage of drier required may be varied to suit manufacturingrequirements for producing dry cloth or other material in a minimum oftime. Or, in some cases, the drier may be omitted.

The method of combining the various ingredients maybe varied in manyways. For example, the temperature and time of heating required forobtaining a particular resinous composition may be varied in accordancewith the differences in the properties of the starting materials.

To form the sheet electrical insulation, the liquid coating compositionor varnish is applied to textile or other fibrous materials (e. g.,cotton, linen, fiber-glass cloth or fabric, etc.) by brushing,sprinkling, spraying or, preferably, by immersion means and undertemperature and other conditions well known to those skilled in the art.Upon heating the coated and impregnated material at a temperature ofabout 110 C. or thereabove, the solvent is evaporated and an insulatingmaterial of low power factor at normal and at elevated temperatures isproduced. It is permanently flexible, is highly resistant to oil,moisture and aging, has a high dielectric strength and a high tearstrength. It has good smoothness or slip and is highly resistant toheat. In testing for heat resistance a sample of the varnished cloth is,heated in a suitable oven at a temperature of about 125 C. and testedfor cracking of the resin film at the end of varying periods of time.This is done by wrapping the cloth around a mandrel of suitable size,for example 0.125 inch in diameter, and noting whether or not the resinfilm has cracked. varnished materials of this invention will standheating at this temperature for from 800 to 1000 hours without crackingof the resin film when tested in the described manner, whereas fabricscoated with the ordinary alkyd resin varnishes when similarly testedshow cracking of the film in approximately 400 hours.

The surprising reduction in power factor obtained by using thepentaerythritol resins instead of glycerol resins is shown by thefollowing comparison of power factors of cloths varnished with resinsmade with pentaerythritol and glycerol:

Power factor at- Type of polyhydric alcohol used in making the resin Theseries 1 resins were prepared from Parts by weight Parts by weightGlycerol 18 Pentaerythritol 20 Soya bean oil fatty acids 60 60 Phthalicanhydride 19 17 Maleic anhydride 3 3 The power factor of the materialsof this invention generally does not exceed substantially 10 per cent at100 C. and usually is considerably less, for instance from 5 to 8 percent As previously described, this low power factor, in

combination with the other desirable properties,

especially adapt these products for the purposes of this invention, thatis, for cable insulation, in insulating electrical coils, and theimproved physical and electrical properties are imparted to theseelectrical structures. The products may replace ordinary varnishedcambric in any of its applications to produce an insulationcharacterized by a high dielectric strength and outstanding resistanceto oil, moisture, abrasion and aging.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

An insulated conductor insulated with a flexible heatand age-resistancevarnished sheet material consisting of a fibrous sheet varnished withthe resinous heat-reaction product of a mixture of ingredientsconsisting by weight, of about 19 parts pentaerythritol, 60 partscottonseed oil fatty acid, 18 parts phthalic anhydride, and 3 partsmaleic anhydride, the said resinous product having an acid number ofabout 5 and the said varnished sheet material having at a temperature of100 degrees C. a power factor not exceeding substantially 10 per cent.

JAMES R. PATTERSON. JAMES R. REID. HENRY A. LE'ITERON.

